The present invention relates to the technical field of adsorptive materials based on activated carbon which have in particular been provided with catalytic and/or reactive constituents.
The present invention relates in particular to an activated carbon as such, in particular an activated carbon which has been provided with reactive and/or catalytic constituents, where the activated carbon is present in the form of discrete activated carbon particles, preferably having a spherical or grain shape, and the activated carbon has been provided with at least one metal component.
In addition, the present invention relates to processes for producing the activated carbon according to the invention which has been provided with at least one metal component.
The present invention additionally relates to uses of the activated carbon of the invention for the production of all types of protective materials and for the production of all types of filters and filter materials. The present invention additionally relates to uses of the activated carbon of the invention as sorption stores for gases or liquids or in the field of catalysis as catalyst or catalyst support or for chemical catalysis. The present invention additionally relates to uses of the activated carbon of the invention in or as gas sensors or in fuel cells and also for sorptive, in particular adsorptive, applications. The present invention also relates to uses of the activated carbon according to the invention for gas purification or gas treatment and also for the removal of pollutants. In addition, the present invention relates to a use of the activated carbon according to the invention for the treatment or provision of clean room atmospheres.
The present invention also relates to protective materials as such which have been produced using the activated carbon according to the invention or comprise the latter. In addition, the present invention relates to filters or filter materials which have been produced using the activated carbon according to the invention or which comprise the activated carbon of the invention.
Finally, the present invention relates to a process for the purification or treatment of gases.
Owing to its quite unspecific adsorptive properties, activated carbon is the most widely used adsorbent. Legal obligations but also the increasing awareness of responsibility for the environment are leading to an increasing demand for activated carbon.
Activated carbon is generally obtained by carbonization (synonymously also referred to as low-temperature carbonization, pyrolysis, burning, etc.) and subsequent activation of carbon-containing starting compounds, with preference being given to starting compounds which lead to economically feasible yields. The weight losses due to elimination of volatile constituents during carbonization and due to subsequent burning during activation are considerable. For further details regarding activated carbon production, preference may be made, for example, to H. v. Kienle and E. Bäder, “Aktivkohle and ihre industrielle Anwendung”, Enke Verlag Stuttgart, 1980.
The nature of the activated carbon produced, viz. fine- or coarse-poured, solid or crumbly, etc., also depends on the starting material. Conventional starting materials are coconut shells, wood charcoal and wood (e.g. wood wastes), peat, hard coal, pitches and also particular plastics which play a particular role in, inter alia, the production of woven activated carbon fabrics.
Activated carbon is used in various forms: powdered carbon, crushed carbon or carbon granules, shaped carbon and since the end of the 1970s also spherical activated carbon (“carbon beads”). Compared to other forms of activated carbon such as powdered carbon, crushed carbon, carbon granules and shaped carbon and the like, spherical carbon has a series of advantages which make it valuable or even indispensable for particular applications: it is free-flowing, abrasion-resistant, free of dust and hard. Owing to their specific shape but also because of the high abrasion resistance, carbon beads are, for example, highly sought after for particular fields of use.
Carbon beads are nowadays usually produced by multistage and very complicated processes. The best-known process comprises production of spheres of hard coal tar pitch and suitable asphalt-type residues from the petrochemicals industry, which are oxidized to make them infusible and subsequently subjected to low-temperature carbonization and activated. For example, the carbon beads can also be produced in a multistage process starting out from bitumen. These multistage processes are very costly and the associated high price of these carbon beads prevents many applications in which the carbon beads would actually have to be preferred because of their properties.
WO 98/07655 A1 describes a process for producing activated carbon spheres, in which a mixture comprising a distillution residue from diisocyanate production, a carbon-containing processing auxiliary and optionally one or more further additives is firstly processed to give free-flowing spheres and the spheres obtained in this way are subsequently carbonized and then activated.
The production of carbon beads by low-temperature carbonization and subsequent activation of new or used ion exchangers containing sulfonic acid groups or by low-temperature carbonization of ion exchanger precursors in the presence of sulfuric acid and subsequent activation, in which the sulfonic acid groups or the sulfuric acid have the function of a crosslinker, is also known from the prior art. Such processes are described, for example, in DE 43 28 219 A1 and in DE 43 04 026 A1 and also in DE 196 00 237 A1 including the German supplementary application DE 196 25 069 A1.
Furthermore, processes in which the production of activated carbon, in particular carbon beads, is carried out by low-temperature carbonization and subsequent activation of sulfonated divinylbenzene-crosslinked polystyrenes (i.e. sulfonated styrene-divinylbenzene copolymers) are known from the prior art (cf., for example, DE 10 2007 050 971 A1).
However, in specific applications, it is not only the geometry and the external shape of the activated carbon which is of critical importance, but also its porosity, in particular the total pore volume and the adsorption capacity and also the distribution of the pores, i.e. the proportion of micropores, mesopores and macropores based on the total pore volume; in particular, the porosity can be controlled by the choice of starting materials and the process conditions. For the purposes of the present invention, the term micropores refers to pores having pore diameters of less than 2 nm, while the term mesopores refers to pores having pore diameters in the range from 2 nm (i.e. 2 nm inclusive) to 50 nm inclusive and the term macropores refers to pores having pore diameters of greater than 50 nm (i.e. >50 nm).
Owing to its good adsorptive properties, activated carbon is used for many applications: thus, activated carbon is used, for example, in medicine or pharmacy and also in the food industry. Activated carbon is also widely used for filter applications (e.g. filtration of gases and liquids, removal of undesirable or harmful or toxic gases, etc.).
In particular, activated carbon can be used in adsorption filter materials, especially in protective materials to protect against poisons such as chemobiological weapons, for example ABC protective clothing. For this purpose, air-permeable and water vapor-permeable protective suits to protect against chemical weapons are particularly well known; such air-permeable and water vapor-permeable protective suits often have an adsorption filter layer comprising activated carbon, which absorb the chemical poisons.
To increase the adsorption performance, permeable adsorptive filter systems, in particular ones based on activated carbon, are often provided with a catalytically active or reactive component by impregnating the activated carbon with, for example, a biocidal or biostatic catalyst, in particular one based on metals or metal compounds.
Such a protective material is described, for example, in DE 195 19 869 A1, which contains a multilayer, textile, gas-permeable filter material having an adsorption layer based on activated carbon, in particular in the form of carbonized fibers, which is impregnated with a catalyst from the group consisting of copper, cadmium, platinum, palladium, mercury and zinc in amounts of from 0.05 to 12% by weight, based on the activated carbon material.
A specific impregnation used in this context is, for example, an ABEK impregnation which has a catalytic or degrading effect in respect of specific toxic substances. In this context, type A relates to particular organic gases and vapors having a boiling point of >65° C., for example cyclohexane. Type B relates to particular inorganic gases and vapors, for example hydrogen cyanide. Type E relates to a degrading or protective action in respect of sulfur dioxide and other acidic gases and vapors. Finally, type K relates to a protective function in respect of ammonia and organic ammonia derivatives. For more detailed information, reference may be made to the relevant European Standard EN 14387 (January 2004).
A disadvantage of conventional impregnations of activated carbon with metals or metal salts is, in particular, the fact that part of the adsorption capacity of the activated carbon, which is required for adsorption and thus for making harmful chemical substances unproblematical, is lost as a result of the impregnation. Thus, the performance of the activated carbon is adversely affected by the processes known from the prior art for impregnating the activated carbon with metals or metal salts. Furthermore, the desired effectiveness is not always achieved by a conventional impregnation. The problem of breakthrough of poisons and chemical weapons at high concentrations is also not always solved by this principle; on the other hand, at very low concentrations of harmful substances or undesirable gases which are to be removed (e.g. in air treatment for clean room conditions), the desired efficiency is often not achieved since adsorption commences only at higher concentrations. Finally, the conventional process of impregnation with metals or metal salts requires relatively larger amounts of the impregnate since a large part of the impregnate present as solid is not available during adsorption, in particular when relatively thick layers of the impregnate are present in the pore system of the activated carbon, in particular in the form of crystallites.